Ocean Thermal Energy Conversion (OTEC) utilizes the temperature difference between warm surface seawater and cold deep seawater to produce electricity via a Rankine cycle. OTEC systems can generate electricity, desalinate water, support aquaculture, and provide refrigeration. While OTEC is a promising renewable energy source that does not emit carbon, its high capital costs and untested commercial scale have prevented widespread adoption.

1. Ocean Thermal Energy
Conversion

2. Content
1. Introduction to OTEC
2. How OTEC Works
3. OTEC Plant Design & Location
4. OTEC Application
5. Benefit of OTEC
6. Potential and Market of OTEC

3. Introduction
• Ocean Thermal Energy Conversion (OTEC) is a process
which utilizes the heat energy stored in the tropical
ocean.
• OTEC utilizes the difference in temperature between
warm surface seawater and cold deep seawater to
produce electricity.
• Because the oceans are continually heated by the sun
and cover nearly 70% of the Earth's surface, this
temperature difference contains a vast amount of solar
energy which could potentially be tapped for human use.

4. Basic Principal
• OTEC is Manifestation of solar energy
• Top layers of ocean receive solar heating
• Bottom layers receive water from polar
regions
• OTEC Uses the vertical temperature gradient
in the ocean as a heat sink/source
• OTEC system is based on the Rankine Cycle

5. Main Component
• Evaporators
• Condensers
• Turbines
• Working fluid
• Cold-water pipe

6. How OTEC Works
• The warm surface ocean water is pumped to the
evaporator, which transfers heat to the working fluid
• Working fluid is turning into a high-pressure vapor.
• The turbine generator spins as the vapor rushes through
it.
• In the low-pressure condenser, the vapor is cooled by
the nearly freezing water brought up from the ocean
depths.
• After condensing, the working fluid is sent back to the
boiler to be reused and to repeat the cycle.

7. Electricity production
• 3 basic OTEC system designs have been
demonstrated to generate electricity:
– Closed cycle
– Open cycle
– Hybrid Cycle

8. Closed Cycled
• In the closed-cycle OTEC system, warm
seawater vaporizes a working fluid, such
as ammonia, flowing through a heat
exchanger (evaporator).
• The vapor expands at moderate
pressures and turns a turbine coupled to
a generator that produces electricity.
• The vapor is then condensed in
condenser using cold seawater pumped
from the ocean's depths through a cold-
water pipe.
• The condensed working fluid is pumped
back to the evaporator to repeat the
cycle.
• The working fluid remains in a closed
system and circulates continuously

9. Open Cycle
• In an open-cycle OTEC system, warm
seawater is the working fluid.
• The warm seawater is "flash"-evaporated
in a vacuum chamber to produce steam at
an absolute pressure of about 2.4
kilopascals (kPa).
• The steam expands through a low-
pressure turbine that is coupled to a
generator to produce electricity.
• The steam exiting the turbine is
condensed by cold seawater pumped from
the ocean's depths through a cold-water
pipe.
• If a surface condenser is used in the
system, the condensed steam remains
separated from the cold seawater and
provides a supply of desalinated water.

10. Hybrid Cycle
• A hybrid cycle combines the features
of both the closed-cycle and open-
cycle systems.
• In a hybrid OTEC system, warm
seawater enters a vacuum chamber
where it is flash-evaporated into
steam, which is similar to the open-
cycle evaporation process.
• The steam vaporizes the working fluid
of a closed-cycle loop on the other
side of an ammonia vaporizer.
• The vaporized fluid then drives a
turbine that produces electricity.
• The steam condenses within the heat
exchanger and provides desalinated
water.

11. OTEC Classification
• Depending on the location
– Land based plant
– Shelf based plant
– Floating plant
– Submerged plant
• Depending on the cycle used
– Open cycle
– Closed cycle
– Hybrid cycle

13. Site Consideration
Factors to be considered while choosing a site:
• Thermal gradient in the ocean
• Topography of the ocean floor
• Meteorological conditions – hurricanes
• Seismic activity
• Availability of personnel to operate the plant
• Infrastructure – airports, harbors, etc.
• Local electricity and desalinated water demand.
• Political, ecological constraints
• Cost and availability of shoreline sites

14. OTEC Application
• Ocean thermal energy conversion (OTEC) systems have many
applications or uses.
• OTEC can be used to :
– generate electricity,
– desalinate water,
– support deep-water mariculture,
– provide refrigeration and air-conditioning
– mineral extraction.
• These complementary products make OTEC systems attractive to
industry and island communities even if the price of oil remains low
• OTEC can also be used to produce methanol, ammonia, hydrogen,
aluminum, chlorine, and other chemicals.

15. OTEC Application

16. Deep-Water-Supported
Mariculture
• Deep-drawn seawater from an OTEC plant is cold, rich in nutrients,
relatively free of pathogens, and available in large quantity.
• It is an excellent medium for growing phytoplankton and
microalgae, which in turn support a variety of commercially valuable
fish and shellfish.
• The large, constant flow of water pumped from an OTEC plant will
reduce disease and contamination in the ponds; marine life,
therefore, can be grown in high densities.
• In addition, deep-drawn cold water can be mixed with warm surface
water, allowing local communities to culture a broad variety of
species.

17. Desalinated Water
• Desalinated water can be produced in open- or hybrid-
cycle plants using surface condensers.
• In a surface condenser, the spent steam is condensed by
indirect contact with the cold seawater.
• This condensate is relatively free of impurities and can
be collected and sold to local communities where natural
freshwater supplies for agriculture or drinking are
limited.

18. Refrigeration and Air-Conditioning
• The cold [5°C (41ºF)] seawater made available
by an OTEC system creates an opportunity to
provide large amounts of cooling to operations
that are related to or close to the plant.
• The cold seawater delivered to an OTEC plant
can be used in chilled-water coils to provide air-
conditioning for buildings.

19. Benefit of OTEC
• No fuel burned , carbon di oxide emission - less than 1%
of fossil fuel plant : has significant potential to provide
clean, cost-effective electricity for the future
• Nutrient rich cold water promotes mariculture
• Produces desalinated water for industrial, agricultural,
and residential uses.
• Cold water for air conditioning
• Fishing - Cold water, drawn from the depths, is nutrient-
rich and can significantly increase fishing yields
• Fresh water production (1 MW plant -> 4500 m3)

20. Disadvantage
• An OTEC facility requires a substantial initial capital outlay
• OTEC has not been demonstrated at full scale over a prolonged
period with integrated power, mariculture, fresh-water, and chill-
water production.
• OTEC is only feasible at relatively isolated sites (deep tropical
oceans); from such sites, the power and marine products must be
transported to market.
• OTEC is ecologically controversial--at least untested--in large scale
and over a long period.

22. Market of OTEC
• Ocean thermal energy conversion (OTEC)
plants may be competitive :
– In the small island with the relatively high
cost of diesel-generated electricity and
desalinated water
– For floating, closed-cycle plants rated at 40
MWe or larger that house a factory or
transmit electricity to shore via a submarine
power cable.

23. Conclussion
• OTEC uses the difference in temperature between warm surface
seawater and cold deep seawater to produce electricity.
• With Ocean cover 70% of earth’s surface that’s absorb sunlight,
OTEC is a prospective alternative source of energy for human
use.
• Beside can be used to generate electricity, OTEC can also be
used to desalinate water, support deep-water mariculture,
provide refrigeration and air-conditioning and mineral
extraction.
• The capital cost of installation is still extremely high and at the
present time the technology remains at the planning/feasibility
study stage.